This invention relates to chain saws, and in particular, to an improvement that enables the chain of a chain saw to be loosened or tightened without requiring loosening of locking nuts that secure a chain-carrying blade of the saw to the motor housing of the saw.
Chain saws include an elongated flat blade having a peripheral edge about which a cutting element, also known as a chain, extends in a continuous, endless loop. The distal free end of the chain is used for cutting. The proximal end of the chain extends around a sprocket gear that engages the chain and causes it to rotate around the peripheral edge of the elongated flat blade when the sprocket gear is rotated. The sprocket gear is attached to the output shaft of a motor means that is housed in a motor housing, and the proximal end of the elongated flat blade is secured to the motor housing.
An elongated slot is formed in the proximal end of the elongated flat blade, and a pair of externally threaded post members that are secured to the motor housing respectively extend through the slot. A pair of internally threaded locking nuts respectively threadingly engage the post members and securely lock the elongated flat blade against movement when the nuts are tightly sealed.
To tighten or loosen the chain, both locking nuts must be loosened. After the blade position is manipulated until the chain is loosened or tightened to a desired taughtness, the locking nuts must then be tightened again. It can take several minutes to perform the above-described procedure. The locking nuts are very tight, and must be loosened and re-tightened with a socket wrench or other high torque tool. This process is awkward and requires strength and a level place to brace the saw. It is not uncommon to drop one of the nuts requiring a search for the nut in the usual debris where chain saw operations generally take place. This further lengthens the time of the adjustment process.
Speed of adjustment may be an important factor in certain applications such as fire fighting where a quick loosening or tightening of the chain is important. Ease of adjustment actually has a safety element to it as chain saw users are likely to continue working with a dangerously loose chain as it stretches during use if it cannot easily be tightened.
The present invention addresses the above problems by providing an improvement to chain saws, wherein a simple cam lever arrangement is provided which permits the loosening and tightening of the chain on the chain saw blade tool with a simple lever motion. The lever arrangement is connected to a distal post member and to the sprocket cover door. Opening the door automatically loosens the chain. Closing the door automatically tightens the chain. Precision adjustments to tension are easily made in the lever arrangement by hand manipulation of a nut on a small threaded cylinder which is free from pressure when the lever is in the release position.